Performance issue in the definititon of testResizeToRangeWithDynamicSpatialShape, chapter_5/research/object_detection/core/preprocessor_test.py(P1)

[DLPerf]

Hello, I found a performance issue in the difinition of testResizeToRangeWithDynamicSpatialShape, chapter_5/research/object_detection/core/preprocessor_test.py. tf.shape will be created repeately in the graph(tensorflow 1.x) during the program execution.It will reduce the efficiency. I think tf.shape should be created before the loop.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.